Sample analyzers such as immunoanalyzers determine the concentration of a component to be measured in a sample by applying a measurement value such as the light absorption to a calibration curve that has been prepared beforehand using a standard sample of known concentration. However, when the concentration of the component in the sample to be measured is too high and exceeds the concentration range covered by the calibration curve, it becomes difficult to accurately determine the concentration of the component to be measured even by applying the measurement value to the calibration curve. In this case, the sample is diluted to obtain a concentration that is within the concentration range covered by the calibration curve, so that the concentration of the component in the sample being measured can be determined by applying the measurement value of the diluted sample to the calibration curve.
Japanese Laid-Open Patent Publication No. 2001-228155 discloses a method of determining antibody or antigen content in serum. According to this method, the concentration of the measurement target component contained in the sample is determined by diluting the sample of unknown concentration by a predetermined factor, applying the measured value of the diluted sample to the calibration curve and converting the measured value to the concentration of the measurement target component in the diluted sample, then multiplying the converted concentration by the dilution ratio in order to obtain the original concentration of the measurement target component contained in the undiluted sample.
Various sources of error are inherent in the diluting measurement of the sample. For example, there is a very small error between the set dilution ratio and the actual dilution ratio when the apparatus dilutes the sample. Dilution may be repeated for a sample of extremely high concentration, and this error may increase according to the repeated dilutions. Furthermore, affinity between a reagent and a diluting solution may produce variance in linearity of dilution. That is, depending on the affinity of the reagent and the diluting solution, the reagent is not necessarily diluted at desired ratio.